In recent years, stricter exhaust gas regulations for vehicles have created a trend aimed at pursuing improved engine efficiency. As the combustion efficiency of engines is improved, the temperature of the exhaust gas tends to increase. Further, there is also a trend toward significantly increased use of superchargers typified by turbochargers. As a result, the components of exhaust manifolds and turbocharger housings and the like require superior heat resistance. It is thought that future trends will see the exhaust gas temperature reaching 1,100° C. Conventionally, if this temperature region is reached, then in many cases, cast steel is used instead of stainless steel sheets, but this results in various problems, including increased weight, a reduction in thermal efficiency due to a larger heat capacity, and a significant reduction in the temperature in the downstream exhaust gas-purifying catalytic converter, resulting in a deterioration in the catalyst efficiency. Accordingly, a stainless steel sheet that can be used at temperatures up to a maximum temperature of 1,100° C. has been keenly sought.
Representative examples of known heat-resistant austenitic stainless steels include SUS310S (25Cr-20Ni) and SUSXM15J1 (19Cr-13Ni-3Si), but it is doubtful that these types of steel could be used in an environment having a maximum temperature of 1,100° C.
Examples of austenitic stainless steels having heat resistance that exceeds that of SUS310S and SUSXM15J1 include a steel disclosed in Patent Document 1 and a steel disclosed in Patent Document 2, but these steels are also not intended for use at temperatures of up to 1,100° C. Accordingly, a stainless steel sheet that can be used at temperatures up to a maximum temperature of 1,100° C. is not currently available.